It is widely accepted that hypoxia and angiogenesis are important factors governing the aggressiveness of tumors. Non-invasive quantitative imaging of these features could lead to improved clinical management and treatment of cancer patients, especially considering recent advances in the clinical application of angiogenesis inhibitors and oxygen-enhancing agents. Therefore, the long-term goal of this application is to develop quantitative MRI methods for the characterization of tumor vascular morphology, function and oxygenation status and to evaluate their role as potential surrogate biomarkers of hypoxia and treatment response. The general hypotheses for this proposal are i) MRI methods that combine the effects of contrast agents with blood oxygenation level dependent (BOLD) measurements can reliably be used to monitor tumor oxygen variations, ii) dynamic susceptibility contrast (DSC)-MRI measures of red blood cell (RBC) flow and distribution will better delineate regions of abnormal vessel physiology as compared to plasma hemodynamic parameters, and iii) a multi-parameter MRI assessment of the tumor microenvironment can differentiate between normoxic and hypoxic tissue. The studies proposed focus on the development and validation of a contrast enhanced BOLD method that has the potential to separate and quantify tumor vascular reactivity and the effects of oxygen modulation. We will evaluate and incorporate corrections for the influence of local tissue pH and hematocrit on these measurements and assess the usefulness of this method to track changes with therapy (Aim 1). The proposed DSC-MRI studies will develop protocols and contrast agents to evaluate red blood cell (RBC) flow, volume, and mean transit time in tumors and compare and contrast these measures to those derived from plasma-distributed contrast agents (Aim 2). The BOLD and DSC-MRI parameters will then be integrated with other physiological measures derived from diffusion-weighted (DW) MRI and PET/CT to provide a quantitative assessment of the underlying mechanisms driving the development of tumor hypoxia (Aim 3). Significance: Once developed and validated these new methods will provide quantitative tools for improving clinical management and for measuring the efficacies of new antiangiogenic and/or oxygen-enhancing treatments.